1. Field of the Invention
The present invention relates to an electrostatic actuator.
2. Description of the Related Art
An electrostatic actuator is a kind of an actuator for driving a movable section by an electrostatic force. The basic construction of the electrostatic actuator is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 8-140367. The electrostatic actuator, which is small and lightweight, can be mounted to, for example, an endoscope, a movable telephone such as a portable telephone, and various PDA (Personal Digital Assistant) for the focusing of the lens system. Such being the situation, the electrostatic actuator attracts keen attentions in recent years.
FIG. 1 is an oblique view showing in a dismantled fashion a conventional electrostatic actuator 100. As shown in FIG. 1, the electrostatic actuator 100 comprises stators 101A, 101B each being in the shape of a flat plate, a movable section 102 made of an electrical conductor and substantially in the form of a parallelepiped, and spacers 103A, 103B each being substantially in the form of a parallelepiped.
The stators 101A, 101B are bonded to the spacers 103A, 103B, respectively, in parallel and apart from each other. The movable section 102 is inserted into the space defined by the stators 101A, 101B and the spacers 103A, 103B such that a gap is provided between the movable section 102 and each of the stators 101A, 101B and the spacers 103A, 103B. It should be noted that the movable section 102 is movable along an imaginary axis A equidistant from the stators 101A, 101B and also equidistant from the axis in the longitudinal direction of each of the spacers 103A and 103B.
Oblong stator electrodes 104A, 104B and 105A, 105B are formed by patterning on the mutually facing surfaces of the stators 101A and 101B, respectively. The stator electrodes 104A, 104B, 105A and 105B are substantially equal to each other in the area. As apparent from the drawing, the stator electrode 104A and the stator electrode 105A are positioned to face each other. Likewise, the stator electrode 104B and the stator electrode 105B are positioned to face each other. Also, the stator electrodes 104A and 104B are arranged along the imaginary axis A and formed apart from each other on both sides of the stator 101A. Likewise, the stator electrodes 105A and 105B are arranged like the stator electrodes 104A and 104B and are shaped equal to the stator electrodes 104A and 104B. It should be noted that the gap between the movable section 102 and each of the stators 101A and 101B is set at about several microns.
If voltage of a predetermined pattern is applied to the stator electrodes 104A, 104B, 105A and 105B, the movable section 102 is moved between the stators 101A and 101B so as to be moved microscopically along the imaginary axis A.
The procedure for moving the movable section 102 will now be described with reference to FIGS. 2 to 4E.
FIG. 2 is a sideward cross sectional view schematically showing the construction of the actuator shown in FIG. 1. FIG. 3A is a waveform diagram showing the voltage pattern of the voltage applied to the stator electrode 105B. FIG. 3B is a waveform diagram showing the voltage pattern of the voltage applied to the stator electrode 105A. FIG. 3C is a waveform diagram showing the voltage pattern of the voltage applied to the stator electrode 104B. Further, FIG. 3D is a waveform diagram showing the voltage pattern of the voltage applied to the stator electrode 104A.
(1) In the first step, voltage V [V] is applied to the stator electrodes 104A, 104B during the time period between time points t0 and t1, as shown in FIGS. 3C and 3D. As a result, the movable section 102 is temporarily attracted to and held by the stator electrodes 104A, 104B by the electrostatic force generated between the stator electrodes 104A and 104B, as shown in FIG. 4A.
(2) In the next step, voltage V [V] is applied to the stator electrode 105B, with voltage V [V] kept applied to the stator electrode 104A, during the time period between time points t1 and t2, as shown in FIGS. 3A and 3D. As a result, one end of the movable section 102 is held by the stator electrode 104A and the movable section 102 is swung about the particular one end in the clockwise direction, as shown in FIG. 4B. In other words, if voltage is applied to the stator electrode 105B with one end of the movable section 102 held by the stator electrode 104A, the other end of the movable section 102 is electrostatically attracted by the stator electrode 105B so as to be held temporarily. It should be noted that the other end of the movable section 102 is slightly moved by a distance xcex4 to the left in FIGS. 4A and 4B, compared with the state (1) shown in FIG. 4A.
(3) Then, voltage V [V] is applied to the stator electrode 105A, with voltage V [V] kept applied to the stator electrode 105B, during the time period between time points t2 and t3, as shown in FIGS. 3A and 3B. As a result, the other end of the movable section 102 is held by the stator electrode 105B, and the movable section 102 is swung about the other end of the movable section 102 in the counterclockwise direction. It follows that the movable section 102 is temporarily held by the stator electrodes 105A and 105B, as shown in FIG. 4C. In other words, since voltage is applied to the stator electrode 105A, with the other end of the movable section 2 held by the stator electrode 105B, one end of the movable section 102 is electrostatically attracted to and held temporarily by the stator electrode 105A. In this case, the movable section 102 is slightly moved to the left in FIG. 4C by a distance 2xcex4, compared with the state shown in FIG. 4A.
(4) Further, voltage V [V] is applied to the stator electrode 104B, with voltage V [V] kept applied to the stator electrode 105B, during the time period between time points t3 and t4, as shown in FIGS. 3B and 3C. As a result, one end of the movable section 102 is held by the stator electrode 105A, and the movable section 102 is swung about said one end in the counterclockwise direction, as shown in FIG. 4D. In other words, since voltage is applied to the stator electrode 104B, with one end of the movable section 102 held by stator electrode 105A, the other end of the movable section 102 is electrostatically attracted to and temporarily held by the stator electrode 104B. In this case, the other end of the movable section 102 is slightly moved to the left in FIG. 4D by a distance 2 xcex4, compared with the state shown in FIG. 4A.
(5) Still further, voltage V [V] is applied to the stator electrode 104A, with voltage V [V] kept applied to the stator electrode 104B during the time period between time points t4 and t5, as shown in FIGS. 3C and 3D. As a result, the other end of the movable section 102 is held by the stator electrode 104B, and the movable section 102 is swung about the other end in the clockwise direction. It follows that the movable section 102 is held temporarily by the stator electrodes 104A and 104B. In other words, since voltage is applied to the stator electrode 104A, with the other end of the movable section 102 kept held by the stator electrode 104B, one end of the movable section 102 is electrostatically attracted to and held temporarily by the stator electrode 104A. In this case, the movable section 102 is slightly moved to the left in FIG. 4E by a distance 2xcex4, compared with the state shown in FIG. 4A.
As described above, it is possible to move the movable section 102 to the left by a desired distance by repeatedly applying the operations described above to the movable section 102.
Incidentally, it is possible to move the movable section 102 to the right in FIGS. 4A to 4E by applying voltage to each of the stator electrodes 104A, 104B, 105A and 105B such that the time is changed from time points t5 to t1, which opposite to the lapse of time shown in FIGS. 3A to 3D.
In the conventional electrostatic actuator of the construction described above, it is certainly possible to move the movable section only within the range in which the movable section can be brought into contact with the stator electrodes. However, it is impossible to move the movable section by a distance larger than the length of the stator electrode, giving rise to the problem that the moving range of the movable section is limited and, thus, the movable section cannot be moved over a wide range.
An object of the present invention is to provide an electrostatic actuator in which the movable section can be moved over a wide range.
According to an aspect of the present invention, there is provided an electrostatic actuator, comprising;
a first stator provided with a first group including first, second and third stator electrodes extending substantially in a predetermined direction, the first stator electrode of the first group being arranged between the second and third stator electrodes of the first group and electrically isolated from the second and third stator electrodes of the first group, and the second and third stator electrodes of the first group being electrically connected to each other;
a second stator arranged to face the first stator with a space therebetween, and provided with a second group including first, second and third stator electrodes extending substantially along the predetermined direction, the first stator electrode of the second group being arranged between the second and third stator electrodes of the second group and being electrically isolated from the second and third stator electrodes of the second group, and the second and third stator electrodes of the second group being electrically connected to each other;
a movable section located in the space to be movable along the predetermined direction and having first and second electrode surfaces which include first and second center regions and are faced to the first and second stators, respectively, the movable section comprising a third group including first, second and third movable section electrodes and extending on the first electrode surfaces substantially in the predetermined direction, and a fourth groups including first, second and third movable section electrodes and extending on the second electrode surface substantially in the predetermined direction, the first centers of the first movable section electrodes of the third and fourth groups being so positioned as to deviate from the first and second center regions in one side of the predetermined direction, respectively, and the second and third centers of the second and third electrodes of the third and fourth groups being so positioned as to deviate from the first and second center regions in the other side of the predetermined direction, respectively.